Parasite control is a vital part of equine care, but fresh research over the past few years has evolved the ways that we should be managing internal parasites. The AgriFutures Thoroughbred Horses Program has unveiled a new pocket guide for all Thoroughbred industry participants that lays out the new best practices for managing the problem of worms.
The old normal
Fixed interval deworming has been the norm amongst horse owners and caretakers worldwide for a long time, but with many operations observing growing resistance to the available deworming drugs and few effective new drugs being developed, new strategies need to be developed to approach deworming schedules.
An AgriFutures-supported study published in 2024 by Abbas et al examined deworming knowledge and practices in Australian Thoroughbred farms, by surveying members of Thoroughbred Breeders Australia. Interval deworming was commonplace, with the largest cohort reporting using deworming products on 7-12-week intervals, selecting the drug used each time by the active ingredient or rotating between products.
While the respondents reported a good understanding of parasite control and what age groups could be most affected by worm-related illnesses, less than 40% were using faecal egg counts to monitor the worm burdens of their herds, and less than half that number were actually making management decisions based on the test results.
Horse deworming | Image courtesy of Western Horseman
While the majority of respondents acknowledged that resistance to anti-parasitic drugs was an important issue, actual knowledge about resistance and ways to effectively counteract worm populations through pasture management was low.
Research suggests that there is currently reported resistance to most available drugs on the market from either of the main types of worm in Australia. Only through changing our approach to deworming practices can we try to turn the tides.
Shifting the mindset
The way forward for parasite control actually involves less drug use than before, with more emphasis placed on effective pasture management and monitoring to ensure that the right drugs are used at the right time.
Resistance to deworming products occurs when worms survive a round of treatment, and over time, this can render a drug ineffective altogether, narrowing the pool of what we can use. By reducing how often we have to use anti-parasitics, we lower the chances of a worm population becoming resistant.
To do this, we have to shift how we look at controlling internal parasites. The new goal is to control the amounts in horses, as opposed to being concerned with eliminating them altogether. The team at Arrowfield Stud, led by Operations Manager Nigel Bentley, have embraced this concept already.
“The less we have to give wormers, the better,” he said. “It’s not only good in terms of minimising resistance, it also reduces costs.”
"The less we have to give wormers, the better." - Nigel Bentley
Test before you treat
Faecal egg counts are effective tests for discovering what sort of worm burden a horse is carrying, including what kinds of worm they could be carrying. What these tests ask of farms and training facilities is fairly simple; a fresh sample of manure from each horse that is being tested.
“The youngstock come in every four weeks for the farrier, so it is easy enough to get a faecal sample when they are in the stable, and then get those samples checked on farm (by the vet team) before they go back out again,” Bentley said.
"The youngstock come in every four weeks for the farrier, so it is easy enough to get a faecal sample when they are in the stable." - Nigel Bentley
By looking at the number of eggs in a manure sample, management can categorise horses in the herd as high or low egg shedders. This helps to identify what paddocks are at higher risk of contamination and, once a horse is identified as either category, treatment regimes can be adjusted appropriately.
Nigel Bentley | Image courtesy Arrowfield Stud
New horses to the property should be quarantined and tested separately from the herd they are going to join to ensure they are put in the right category.
“Any new stock that arrives on the farm will have a faecal sample taken on the day they arrive in quarantine, and then if that indicates they need worming, we can worm them while they’re still in quarantine,” Bentley said. “We then take another sample two weeks later while they are still in quarantine to make sure the wormer has worked as intended.”
Right product, right dose
The emphasis on giving the right paste at the right time of year in the right dose is about more than just controlling the parasite population with a specific horse; it is about cost efficiency and conserving the products we have. Some products experience widespread resistance already in Australia, and the number of new products coming to the market is minimal.
It is recommended to weigh horses before worming to ascertain the correct dosage and communicate with your vet about what product to use. Getting these things right in an operation the size of Arrowfield means huge savings in both time and on the balance sheet.
“For people who are still drenching every four to six weeks, not only is it overuse of the pastes available, it is a huge expense,” Bentley said. “When we can push it out to a minimum of 12 weeks with careful monitoring, that is great. At the moment, most of our mares only require worming once or twice a year, which is a big saving.
“We usually give youngstock their first drench when they are 10 to 12 weeks old, and then they receive a second drench around the 20-week mark. And from then on until they go to the sales, every 12 weeks we will do a faecal egg count and worm them if necessary. The type of wormer depends on the weather, the time of year, and how the season has been. We liaise with the vets all of the time on which one to give as young stock may need a different wormer to older stock.
"We liaise with the vets all of the time on which one to give as youngstock may need a different wormer to older stock." - Nigel Bentley
“We also use Bioworma. All of the weanlings are fed Bioworma, which will be fed until late autumn when the weather starts to cool off.”
Bioworma uses the spores of the Duddingtonia flagrans fungus to consume roundworm larvae, and is an additional tool at Arrowfield’s disposal that helps to minimise how often they need to worm.
Bioworma | Image courtesy of International Animal Health Products
Beyond the paste
As outlined in the aforementioned study, most farms understand the importance of pasture care and rotation in small paddocks, but the same diligence needs to be applied to larger areas.
“Stock rotation is a big part of management as well,” Bentley said. “We have cattle that rotate through the paddocks as well. We pick up yards daily, and horses that are on yard rest are also fed Bioworma.”
"Stock rotation is a big part of management as well." - Nigel Bentley
Observation of a horse’s condition is already part of stud and stable staff’s every day routine, and making staff aware of the signs of worm-related illness leads to earlier detection of a worm burden. Bentley and the management team ensure that staff have the knowledge to catch things early.
“We have weekly meetings with staff to teach staff about different things to look out for,” he said. “Each week is a different topic, for instance the next one will be on wound care protocols, and we recently had a meeting to learn about worming protocols.”
The new pocket guides for the public and vets make it easy for operations to get everyone on the same page.
